Following the discovery by Grenoble (U.S. Pat. No. 3,905,842 granted Sept. 16, 1975 and assigned to the assignee hereof) that boron is effective in small but critical amount and in critical proportion to nitrogen in silicon-iron to promote secondary recrystallization during the final texture-developing anneal, Maucione (U.S. Pat. Application Ser. No. 677,147, filed Apr. 15, 1976 and also assigned to the assignee hereof) found that the presence of a very small amount of boron in the coating on such a boron-containing steel further promotes secondary recrystallization and development of still better magnetic properties in the ultimate product. Maucione further found that the presence of boron in the coating can cause secondary recrystallization to take place when it otherwise would not, and also discovered that the presence of boron in the insulating coating was not effective in causing or promoting secondary recrystallization in the absence of boron in the metal itself at the outset of the final anneal.
In the practice of Maucione's teachings, boron has been incorporated in the refractory oxide coating, usually magnesium hydroxide [Mg(OH).sub.2 ], provided in accordance with the process disclosed and claimed by McQuade in U.S. Pat. No. 3,054,732 by a dipping operation or by brushing a solution of a suitable boron compound on the coating, or even spraying it on.
Then, through the discovery by Arendt and Aubourg that a boron-containing compound and Mg(OH).sub.2 can be electrolytically codeposited as described and claimed in their patent application referred to above, it became possible to exercise better control over the amount of boron incorporated in the insulating coating and also to more uniformly distribute the boron throughout the coating. As another important advantage of this codeposition method, the resulting product has a surface which is more amenable to fabrication operations customarily involved in the use of electrical steel.